Microwave antenna



Oct-l5, 1946. A. c. BECK MICROWAVE ANTENNA Filed Aug. 19, 1942 3Sheets-Shet 1 m a 3 m 31.. air. \/A a a H M EH M W l l A I L lv 7 M u Mmlliiflll a t L 2 INVENTOR AC. BECK :P I mam summer .T Y A G K B 0d. 15,1946. c BECK MICROWAVE ANTENNA Filed Aug. 19. 1942 3 Sheets-Sheet 2 FIG.2.

INVENTOR AC. BECK ATTORNEY Oct. 15, 1946. A. c. BECK.

MICROWAVE ANTENNA Filed Aug. 19, 1942 3 Sheets-Sheet 3 'D '15 --?0 .50ROI/ID TMPDM'CTIVE CHARACTERISTIC ELETRIC PLANE INVENTOR AC. BECK A TTORNEY Patented Oct. 15, 1946 MICROWAVE ANTENNA Alfred 0. Beck, RedBank, N. J., assignor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application August 19, 1942,Serial No. 455,322 '12 Claims. (01. 250-11) This invention relates todirective antenna systems and particularly to antenna systems of thetype utilized in radio range and direction finding systems.

As is known, the peak or nose of the maximum lobe of highly unidirectiveantennas commonly employed for telegraph and telephone communication isrelatively blunt or flat over an appreciable angular range of wavedirections and is ordinarily not suificlently pointed or sharp to selectone of the several distinct directions included in the aforementionedrange. Also, as is known, at least three distinct antenna arrangementshave been suggested for obtaining, in the short wave (10 to 200 meters)and ultra-short wave (1 to 10 meters) fields, a greater degree ofdirective selectivity than that provided by the so-called signalantennas and, in particular, for securing the high degree of directivesensitivity required in radio direction finding systems of the airportlanding, radio range (radar) and radio scanning types. Thus, Figs. 2 and3 of Patent 2083,242 to W. Runge illustrate respectively a lobe-rotationor conical scanning system and a lobe-sweeping system; and Patents2,217,321 to W. Runge and 2,002,181 to W. Ilberg illustratelobe-switching arrangements. While these arrangements have performedfairly satisfactorily in the short and ultra-short wave fields they arenot readily adapted for use in the microwave field (below 1 meter). Itnow appears desirable to secure a microwave antenna system having a highdirective sensitivity and, in particular, to secure an efiicientcentimeter antenna of the lobe-switching type which may be employed inthe direction finding systems mentioned above.

It is one object of this invention to determine accurately thepropagation direction of a radio wave.

It is another object of this invention to energize or illuminateefliciently, and for maximum gain, a microwave concave type reflector.

It is still another object of this invention to utilize, in a lobeswitching radio scanning system, waves polarized in the scanning plane.

It is a further object of this invention to obtain a two-position lobeswitching microwave scanning antenna arrangement having a highdirectional sensitivity.

It is still another object of this invention to eliminate reflectionlosses in a transmission system comprising two air-filled wave guidesconnected together through a solid dielectric channel.

In accordance with the preferred embodiment 2 of the invention a pair ofbranch vertical rec tangular wave guides, each having side walls ofdifferent dimensions, an open'end and a closed end, are positionedadjacent to each other. The corresponding open ends are connectedthrough a wave guide switch of the type disclosed in the copendingapplication of A. G. Fox, Serial No. 422,408, filed December 10, 1941,to a main cylindrical wave guide and a translation device such as aradio range transceiver of the pulse type. The parallel guides each havean aperture in one of the narrow walls adjacent the closed end, the twoapertures being in the same plane so that their directions of maximumaction are parallel to each other and perpendicular to the plane of theapertures. A paraboloidal reflector having its focus between the twoapertures is utilized for changingthe parallel directions of action toangularly related directions extending in the desired horizontalscanning plane at equal angles to the reflector axis. In operation, asubstantial amount of the energy propagated through each apertureimpinges on the reflector and the energy distribution over the reflectoris, by reason of the relative sizes of the aperture and the reflectorand the spacing therebetween, fairly uniform. The wave guide switchfunctions to render the parallel branch guides alternately inactive,whereby the maximum lobe for the entire system is switched between twopredetermined positions in the horizontal scanning plane. Also, theconnection between the parallel guides and the transceiver is such thatthe wavelets conveyed by each of the parallel branch guides arepolarized perpendicular to the longitudinal guide axis and in the planeof the guide apertures. Hence, the wave components projected orcollected by the system are polarized in the lobe switching or scanningplane and highly satisfactory reflected pulses are received,particularly in short range scanning operations.

The invention will be more fully understood from a perusal of thefollowing specification taken in conjunction with the drawings on whichlike reference characters denote elements of similar function and onwhich:

Figs. 1, 2 and 3 illustrate, respectively, a crosssectional front view,a cross-sectional partial side view and a cross-sectional partial topview of the preferred embodiment of the invention;

Figs. 4 and 5 are curve illustrating the measured directivecharacteristics of a system constructed in accordance with theinvention;

Figs. 6, 7, 8, 9 and 10 illustrate vertical branch wave guidearrangements any of which may be substituted for that included in thepreferred embodiment.

Referring to the drawings, the preferred embodiment illustrated by Figs.1, 2 and 3 is especial- 1y designed for installation in a submarine, butit should be understood the invention may be incorporated in apparatusinstalled on other types of mobile bodies or at a fixed station. InFig. 1. reference numeral denotes a translation device comprising atransceiver of the pulse type commonly employed in the radio rangingsystems. Numeral 2 designates a horizontal rectangular wave guideconnected to the transceiver and having a narrow electric plane side,hereinafter called the a wall, and a wide magnetic plane side,hereinafter called the b wall. Guide 2 is connected to a verticalcylindrical guide 3 through an antenna coupling arrangement comprisingthe pick-up or receiving antenna 4 positioned within guide 2 parallel tothe narrow walls a, an exciter or transmitting doublet antenna 5positioned within and aligned with a diameter of guide 3, and a coaxialline 5 comprising an outer and an inner conductor. The outer conductoris formed by tubularsurfaces I and 8 of cylindrical block member 9, andthe inner conductor is formed by the two colinear plugs l and H mountedinside the sleeve |2. Plug l0 and sleeve I2 are each rotatable. The twoend sleeve portions or sections overlapping plugs l0 and II are eachapproximately a quarter wave-length long, so that each plug is connectedto the sleeve through an open quarter wave line having a zero impedance,substantially.

The pick-up antenna 4 is tuned by means of a variable coaxial tuner l3comprising a shortcircuiting adjustable disc I4; and the load end ofguide 2 is terminated in a movable reflecting piston l5, whereby theresonant length of the pick-up antenna 4, and the spacing betweenantenna 4 and the reflector l5, may be adjusted, in accordance with themanner now well understood in the art, for optimum transfer of energybetween guide 2 and antenna 4. The unbalanced coaxial line 6 isconnected to the balanced dipole through a balance-to-unbalance couplingcircuit comprising the quarter wave vertical cylindrical surface I6 ofmember 9, the quarter wave vertical cylindrical surface l1 and thehorizontal annular short-circuiting surface or connection I3. Each halfof dipole 5 extends beyond the wall of circular guide 3 and into asocket or recessed section |9 comprising the surface 20 of member 9, thesurface 2| of tubular member 22 and the disc member 23. The depth orlength of each of sections I9 is such that dipole 5 has the properlength for optimum resonance. Reference numeral 24 designates a remotelycontrolled, manually driven worm which is associated through worm gear25 with member 22, for

4 The uppermost end of guide 3 is connected to the lower end of a waveguide switch of the type disclosed in the aforementioned copendingapplication of A. G. Fox. Switch 3|! comprises two parallel wave guidetuned sections 3| and 32, each having orifices 33 and 34, detuningmember 35 which is rotated about shaft 38 by means of a motor (notillustrated), as indicated by arrow 31. If desired, an additional set oftuned sections may be included in switch 30, between sections 3|, 32 andguide 3, for the purpose of increasing the band width characteristic ofthe switch. The upper end of switch 30 is connected to a pair ofparallel branch rectangular wave guides 33 and 35 having the common 17or wide wall 40 and the flat end pieces 4| and 42, respectively. Thenarrow transverse dimensions, or a walls, of the tuning guide sections3| and 32 and of branch guides 38 and 39, are positioned parallel to thedoublet 5 for utilization of the transverse electric wave componentrepresented by arrows 43. Reference numerals 44 and designaterectangular antenna apertures positioned adjacent the cover or endpieces 4| and 42 and in the back narrow walls 45 and 41 (Fig. 3) ofguides 38 and 39. Apertures 44 and 45 are equipped with a commonwater-tight polystyrene member 48. The vertical portion of the rotatablestructure is preferably enclosed in a tubular shield 43 having a largeaperture opposite apertures 44 and 45.

Referring particularly to Figs. 2 and 3, reference numeral denotes asection of a paraboloidal reflector facing apertures 44 and 45 andhaving a horizontal axis 5| and a finite focus 52 positioned betweenapertures 44 and 45. The reflector 50 is attached by two brackets 53 tothe tubular shield member 45 so that the antenna apertures 44 and 45 andreflector 50 may be rotated as a unit for radio range searchingpurposes. While a sectional paraboloidal reflector having the plane 54of its opening spaced from I the reflector focus 52 is preferablyemployed in smoothly rotating the vertical portion of the structureincluding the entire cylindrical guide 3. the bearing or plane ofrotation being denoted by numeral 26. As is apparent, during therotation, plug In of the inner conductor of coaxial line 6 rotatesrelative to plug l and the contiguous tubular surface 8 of the outerconductor of line 6 rotates relative to each other.

Reference numeral 21 denotes a heavy tapered cylindrical polystyreneplug which, as explained below, has a critical length and is attached orfitted to the inner surface 28 of the guide wall member 22 at a point ashort distance above doublet 5 by means of the cylindrical member 29,the junction or connection being water-tight order to secure a wideangle directive lobe in the vertical plane and a narrow angle lobe inthe horizontal plane, if desired, a conventional paraboloidal reflectorhaving a circular cross section may be utilized. In accordance with theinvention the focal length of the reflector, the reflecting area of thereflector and the aperture areas are selected to obtain optimumenergization of the sectional reflector. Considered from. a mechanicalstandpoint the structure is exceedingly rugged and is designed towithstand heavy water pressure. Thus, the polystyrene member 48 isrelatively thick and strong, and functions to prevent water fromentering guide 3 when the submarine is submerged. Inaddition thepolystyrene plug 21 is solidly embedded or fitted to the member 28 sothat in the event of breakage of member 48 water is prevented fromentering horizontal guide 2. Since water may leak into vertical guide 3or may condense therein, a drain I 55 is preferably provided at thebottom of the styrene plug 21, and at the junction 51 of plug 21 and theupper portion of guide 3. Preferably, the electrical length L of plug 21is made equivalent to approximately a multiple of a half wavelength sothat the two reflected waves propagated back into guide 3 mutuallycancel. After passing through the polystyrene channel 21 the waves -areconveyed through the upper portion of cylindrical guide 3 to sections 3|and 32 of wave guide switch 30. As explained in the A. G. Foxapplication mentioned above, the radial rotating member 35 functions todetune, alternately, sections 3| and 32 and thereby to blocksuccessively the flow of energy in these sections. Hence, dependent uponthe position of member 35, energy in the form of a train of pulses flowsthrough one or the other of the branch guides 3| and 32 to one or theother of the apertures 44 and 45. The horizontally polarized wavesissuing alternately from apertures 44 and 45 impinge upon reflector 50,the directions 58 and 59 of maximum action, respectively, for theelemental antenna. apertures 44 and 45, being parallel and substantiallyperpendicular to the plane of the apertures or member 48. Reflector 50functions, in effect, to bend or change the two parallel propagationdirections 53 and 59 to the diverging directions 60 and 8|,respectively, which make equal angles with the parabolic reflector axisas shown in Fig. 3.

. The maximum direction 60 of radiation for the combined systemcomprising the left-hand aperture 44, as viewed from reflector 50, andof reflector 50, is positioned at the right of the reflector axis 5|,and the maximum direction 3| for the system comprising the right-handapertur 45 and reflector 50 is positioned at the left of axis 5|.Assuming axis 5| of the antenna system is aligned with a reflectivetarget the pulse train is returned to the reflector 50 and conveyed tothe transceiver successively through dielectric channels 3| and 32, thereceiving action of the system being reciprocaLto the transmittingaction.

Referring to Figs. 4 and 5 the curves illustrate respectively, the twosingle trip and the two round trip" directive characteristics taken inthe horizontal scanning plane, that is, in the electric plane of thewave component, for a system constructed in-accordance with theinvention. Curves 62 and 53 illustrate the single and round tripcharacteristics for aperture 44 with reflector 50, and curves 34 and 65illustrate the corresponding characteristics for aperture 45 andreflector 50. The single trip characteristics are conventional directivecharacteristics which may be determined by measuring the fieldestablished by the antenna or by measuring the response of the antennato incoming waves. The round trip characteristic, which is of importancein object location systems, may be obtained by utilizing a target spacedfrom the antenna, transmitting pulses from the antenna while rotatingthe antenna through 360 degrees and noting the relative intensity of thereceived pulses. It should be noted that the minor lobes of both thesingle trip and the round trip characteristics are negligible, as isadvantageous in object location systems. More specifically, in scanningsystems successful operation can not be secured with antennas havinglarge minor lobes since ambiguous indications are obtained. On the otherhand, while pronounced minor lobes are undesirable in signal systems,satisfactory intelligence communication may be secured with antennashaving large secondary lobes. As shown by Figs. 4 and 5 theratio, inapplicants system, of the intensity of the maximum lobe to the intensityof the largest minor lobe is high, that is, in the order of 5. The minorlobe suppression is secured, in accordance with the invention, in partby using a unidirective wave guide aperture adjacent the focus of thereflector for eiflciently illuminating the reflector. In addition, inaccordance with the invention, the waves utilized in the horizontalplane lobe switching system of the invention are polarized in thescanning or lobe switching plane. By using horizontally polarized waves,in a horizontal plane lobe switching system installed on a ship orsubmarine, undesired pulse reflections from ocean waves are renderednegligible and of small intensity as compared to those obtained whenvertically polarized waves are employed. Stated differently, inaccordance with the invention, the false indications produced byundesired reflection from ocean waves, and ordinarily very pronouncedduring target searching operations at close range (300 yards), areminimized.

Referring to Fig. 6, reference numerals 36 and 6! denote end reflectormembers which may be employed in the structure of Fig. 1 in place of thetop end members 4| and 42, respectively, and which are inclined at anangle of 45 degrees relative to the vertical walls of the branch guides38 and 39. In Fig. '7 reference numerals 63 and 69 denote curvedreflector members which may be used in place of the end reflectors 4|and 42. In Fig. 8 numerals l0 and 1| denote shield members which may beadded to the horizontal reflector members 4| and 42 of Fig. 1. Thestructures illustrated by Figs. 9 and 10 are each the same as thatillustrated by Fig. 1, except that in the structure of Fig. 9 the branchguides 38 and 39 are tilted away from reflector 50 and make an angle of5 degrees with the vertical and, in the structure of Fig. 10, the guidesare tilted toward the reflector 50 and make an angle of 25 degrees withthe vertical. While the attenuation and reflection losses occasioned bythe bend or corner 13, Fig. 2, are avoided by employing the curvedreflector of Fig. 7, and are almost eliminated by using the arrangementof Fig. 6, and while the structures illustrated by Figs. 6 to 10,inclusive, may produce a more nearly flat wave front and may efl'ect areduction in secondary lobes,'it has been found by experiment that theadvantage gained by utilizing the arrangements of Figs. 6 to 10 is notlarge and that for all practical purposes the system of Fig. l is highlysatisfactory.

Although the invention has been explained in connection with certainembodiments thereof, it should be understood that it is not to belimited to the embodiments described since other apparatus maysuccessively be employed in practicing the invention.

What is claimed is:

1. An antenna system comprising a pair of wave guides each having aseparate aperture for emitting and collecting radiant energy. a concavereflector facing the separate apertures and having a focus positionedbetween said apertures.

2. An antenna lobe switching system comprising a concave reflectorhaving a finite focus, a pair of antenna elements equally spaced fromsaid focus, each of said elements comprising a wave guide having anaperture facing said reflector.

and means for alternately connecting a transceiver to said guides.

3. In combination, a parabolic reflector having a focus, a pair ofunidirective antenna elements facing said reflector and equally spacedfrom said focus. said elements each comprising an aperture 7 in the sidewall of a dielectric guide, and means for alternately energizing saidelements.

4. A combination in accordance with claim'S, and reflecting members forclosing the end of said guides adjacent said apertures, said membersbeing inclined at 45 degrees to said wall and facing the parabolicreflector.

5. A combination in accordance with claim 3. and reflecting members forclosing the ends of said guides adjacent said apertures, said membershaving a curved surface facing said parabolic reflector.

8. An antenna lobe switching system for scanning in a given planecomprising a parabolic reflector having a flnite focus, a pair ofantenna elements equally spaced from said focus, said elements beingincluded in the focal plane of said reflector and in the desiredscanning plane, said elements comprising rectangular wave guides eachhaving an aperture facing said reflector and located in correspondingnarrow side walls of said guides, and means for alternately energizingsaid guides with waves polarized in the plane of said wall.

7. A lobe switching antenna system comprising a pair of parallelrectangular wave guides each having a side aperture at one end, aconcave reflector facing said apertures and having its axisperpendicular thereto, said apertures being equally spaced from saidaxis, and means for connecting a transceiver alternately to the otherend of said guides. L

8. An antenna lobe switching system comprising a'pair of wave guides, atranslation device, and means for alternately connecting said device tocorresponding ends of said guides. said guides each having a sideaperture adjacent the other end, said apertures facing the same compasspoint direction and having parallel directions of maximum action, and aconcave reflector facing said apertures, said reflector having aprincipal axis parallel to said direction and a focus symmetricallydisposed relative to said apertures, whereby said parallel directions ofaction are changed to directions making equal angles with said axis andthe wavelets emitted and collected by said apertures and impinging onsaid reflector ,travel alternately in propagation directions makingequal angles with said axis.

9. A lobe switching microwave antenna comprising a paraboloidalreflector. a pair of wave 8 guides having apertures facing saidreflector and equally spaced from the reflector focus, a transceiverconnected to said guides, and switching means for alternately renderingsaid guides nonconductive.

10. A microwave antenna system for scanning in a given plane comprisinga concave reflector having aflnite focus. means for emitting and collecting alternately at two points equally spaced from said focus in thereflector focal plane waves polarized in said plane, said meanscomprising a pair of rectangular wave guides connected at one end to atransceiver through a wave guide switch, said guides having squareapertures at said points, and said apertures being included in theelectric plane of said guides.

11. An antenna system comprising a pair of I quadrilateral wave guideshaving sides of different dimensions, said guides being open at one endand closed at the other, means connected to the open ends for supplyingor receiving microwaves polarized in the plane of the short side, anaperture in one narrow side of each guide adjacent the closed end, and aconcave reflector facing said aperture and having its axis and directionof maximum radio action positioned perpendicular to the plane of saidapertures, whereby waves emitted or collected by said system arepolarized in the plane of maximum wave propagation.

12. A microwave lobe switching antenna system comprising a pair ofparallel quadrilateral dielectric channels having one pair ofcorresponding ends closed and the other pair open, a transceiver, meansfor alternately transferring'between the transceiver and the open endsof said channel wavelets polarized linearly in a polarization planecontaining one side of each guide, said wavelets being polarizedperpendicularly to the longitudinal axes of said channels, each guidehaving an aperture in said side at its closed end, a paraboloidalreflector having its axis perpendicular to the polarization plane andits focus positioned in said plane between said apertures, whereby themaximum directive lobe of said system is successively aligned with twoangularly related direcplane.

Almllil) C. BECK.

